The present invention relates to a so-called retrofocus type wide angle zoom lens which is composed of a divergent front lens group and a convergent rear lens group which are mechanically moved to thereby vary the focal length.
Recently, zoom lenses for 35 mm single lens reflex cameras have extensively been used, and there have been strong demands for super compact lens systems in view of their portability.
On the other hand, in the zoom lenses, in order to meet the requirements that various aberrations be well corrected from the minimum focal length to the maximum focal length with a good balance, the diameter of the front lens be decreased to thereby miniaturize the overall lens system, and further the lens system be made to have a wide view angle, it is general to increase a refractive index of each lens, which leads to an expensive lens.
The present invention provides as an object a high performance zoom lens of wide angle, in which a view angle at the minimum focal length covers a wide angle of 85.degree., a zoom ratio is approximately two, a diameter of a front lens is about 0.88F.sub.s which means a very compact physical size, and negative lenses included in the front lens group which is expensive because of its relatively large diameter have low refractive indexes, which leads to an economical lens.
In Japanese Laid-Open Patent Application No. 119919/79 is disclosed a very compact wide angle two lens group type zoom lens in which a view angle at the minimum focal length covers a wide angle 85.degree., a zoom ratio is approximately two and a diameter of the front lens is about 0.88F.sub.s. In this proposed lens, in order to decrease the number of the lens elements forming the front lens group in compliance with miniaturization, a first lens which is closest to the object must have a refractive index more than 1.8. As noted in the examples of the publication, refractive indexes of negative lenses included in the front lens group which has a large diameter are high as a result of which the lens system is expensive disadvantageously.